1. Field of the Invention
The present invention relates to a projecting apparatus suitable for, e.g., a color liquid crystal projector for enlarging and projecting image information displayed on one or a plurality of optical modulation elements such as liquid crystal panels on a screen or the like.
2. Related Background Art
A variety of color liquid crystal projectors for projecting image information displayed on a liquid crystal panel as an optical modulation element on a screen are conventionally proposed. An optical system for a liquid crystal projector using a transmission liquid crystal is proposed, i.e., Japanese Laid-Open Patent Application No. 61-99118. FIG. 1 is a view schematically showing the optical system of this prior art.
Referring to FIG. 1, light emitted by a light source 1 is roughly collimated by a reflector 2 (parabolic mirror) and incident on a dichroic mirror 34 which transmits the blue light component (B light component) and reflects the green light component (G light component) and the red light component (R light component). The G and R light components reflected by the dichroic mirror 34 enter a dichroic mirror 35 which reflects the green light component (G light component) and transmits the red light component (R light component). The green light component reflected by the dichroic mirror 35 illuminates a liquid crystal panel 14 for G light, and the red light component transmitted through the dichroic mirror 35 illuminates a liquid crystal panel 15 for R light. The blue light component transmitted through the dichroic mirror 34 illuminates a liquid crystal panel 16 for B light.
The light beams transmitted through the liquid crystal panels 14, 15, and 16 are modulated in accordance with image information in units of colors. The light beams from the liquid crystal panels 14 and 16 are synthesized by a dichroic mirror 37 which transmits a blue light component and reflects a green light component. The red light component from the liquid crystal panel 15 passes through a mirror 38 and reaches a dichroic mirror 39 which transmits a red light component and reflects blue and green light components.
The red, blue, and green light components are synthesized by the dichroic mirror 39 into a full-color image. This full-color image is projected on a screen 23 through a projection optical system 48. The liquid crystal panels 14 to 16 use, e.g., a twisted nematic (TN) liquid crystal or a super twisted nematic (STN) liquid crystal.
FIG. 2 is a view schematically showing an optical system for a color liquid crystal projector using a transmission liquid crystal proposed in Japanese Laid-Open Patent Application No. 1-131593.
Referring to FIG. 2, light emitted by a light source 1 is roughly collimated by a reflector 2 (parabolic mirror) and incident on a dichroic mirror 34' which reflects a blue light component (B light component) and transmits a green light component (G light component) and a red light component (R light component). The light components transmitted through the dichroic mirror 34' are incident on a dichroic mirror 35' which transmits the green light component and reflects the red light component. The green light component transmitted through the dichroic mirror 35' illuminates a liquid crystal panel 14 for green, and the red light component reflected by the dichroic mirror 35' illuminates a liquid crystal panel 15 for red through mirrors 38 and 41. The blue light component reflected by the dichroic mirror 34' illuminates a liquid crystal panel 16 for blue through mirrors 36 and 40.
The light beams transmitted through the liquid crystal panels 14, 15, and 16 are modulated in accordance with image information in units of colors. The light beams reach a cross dichroic prism 42 and synthesized into a full-color image. The cross dichroic prism 42 is formed by crossing a dichroic mirror for transmitting a green light component and reflecting a blue light component and a dichroic mirror for transmitting a green light component and reflecting a red light component. The full-color image synthesized by the cross dichroic prism 42 is projected on a screen 23 through a projection optical system 48.
FIGS. 3 and 4 are views schematically showing color projectors each using an optical system for synthesizing a full-color image without using a plurality of flat dichroic mirrors or prisms, which are proposed in Japanese Laid-Open Patent Application No. 4-428.
In FIG. 3, transmission liquid crystal panels 14, 15, and 16 are illuminated with light beams in corresponding wavelength bands. Light beams transmitted through the liquid crystal panels and modulated according to image information in units of colors are brought to a focus near the stop of a projecting lens 48 through field lenses 45, 46, and 47 arranged behind the liquid crystal panels. Tilted mirrors 20 and 21 are inserted near the stop of the projecting lens 48 at an interval. The light beam transmitted through the liquid crystal panel 14 passes between the two mirrors.
The liquid crystal panel 15 and the field lens 46 are decentered from each other by a distance s and so are the liquid crystal panel 16 and the field lens 47. The light beam transmitted through the liquid crystal panel 15 is deflected through the field lens 46 and reflected by the mirror 20.
Similarly, the light beam transmitted through the liquid crystal panel 16 is deflected through the field lens 47 and reflected by the mirror 21. The color light components are transmitted through the projecting lens 48, synthesized into a full-color image, and projected on a screen 23.
In FIG. 4, the positions of each liquid crystal panel and a corresponding field lens are reversed to those in FIG. 3. In this case as well, a liquid crystal panel 15 and a field lens 46' are decentered from each other by a distance s', and so are a liquid crystal panel 16 and a field lens 47'. The light beam deflected through the field lens 46' is focused, transmitted through the liquid crystal panel 15, and reflected by a mirror 20.
Likewise, the light beam deflected through the field lens 47' is focused, transmitted through the liquid crystal panel 16, and reflected by a mirror 21. The color light components are transmitted through a projecting lens 48, synthesized into a full-color image, and projected on a screen 23.
FIG. 5 is a view schematically showing an optical system for a color liquid crystal projector using the reflection liquid crystal proposed in Japanese Laid-Open Patent Application No. 6-265842. This optical system is called a Schlieren optical system.
Referring to FIG. 5, light emitted by a light source 1 is roughly collimated by a reflector 2 (parabolic mirror), reflected by a mirror 36, and condensed through a condenser lens 4 to form a light source image near a reflection mirror 43 arranged at the position of the aperture stop of a projecting lens 48. The light beam is reflected by the reflection mirror 43 toward a plano-convex lens 44, collimated by the plano-convex lens 44, and separated into three colors by a cross dichroic prism 42. The three color light components respectively illuminate reflection liquid crystal panels 25, 26, and 27 of the corresponding wavelength bands.
The light beams modulated by the reflection liquid crystal panels 25 to 27 are synthesized into a full-color image by the cross dichroic prism 42. The full-color image is focused by the plano-convex lens 44, passes through a stop 28, and is projected on a screen 23 through the projecting lens 48.
A liquid crystal, e.g., a polymer dispersed liquid crystal is sealed in each liquid crystal panel. When the white level is to be displayed, the liquid crystal panel becomes transparent to reflect an incoming light beam. In displaying the black level, it scatters the light beam. The light components reflected by the liquid crystal panels and synthesized by the cross dichroic prism 42 are focused near the stop 28 of the projecting lens 48 through the plano-convex lens 44. Most light components reflected by the liquid crystal panels pass through the aperture of the stop 28 to display the white level on the screen 23 through the projecting lens 48. However, only a few of light beams scattered by the liquid crystal panels pass through the aperture of the stop 28 to display the black level on the screen 23.
Image information is displayed using scattering in liquid crystal panels and displayed on the screen through the projecting lens.
The conventional color liquid crystal projectors shown in FIGS. 1 to 5 have the following problems.
The optical system shown in FIG. 1 cannot achieve color separation and synthesis without four dichroic mirrors (34, 35, 37, and 38) which are hard to manufacture. Additionally, the flat dichroic mirrors 39 and 37 must be arranged tilted between the projecting lens 48 and the liquid crystal panels 15 and 16, respectively. Astigmatism generated by the dichroic mirrors 37 and 39 degrades the projected image. If the resolution of the liquid crystal panel is low, the astigmatism can be ignored, but it is a problem in a high-resolution liquid crystal projector.
The color liquid crystal projector shown in FIG. 2 solves the above problem of astigmatism. In FIG. 2, the cross dichroic prism 42 is used in the color synthesis optical system, thereby preventing astigmatism. However, the cross dichroic prism 42 is more difficult to manufacture than the flat dichroic mirrors used in the color synthesis optical system shown in FIG. 1. This is because the prism vertical angle process accuracy, prism joint accuracy, prism refractive index, and the like must be strictly managed to prevent the projected image from being discontinuous at the four prism joint portions.
To obtain desired characteristics, the dichroic mirror film must have a multilayered structure having a larger number of layers than that of the flat dichroic mirror. This also results in difficulty in manufacturing.
In the color projectors shown in FIGS. 3 and 4, the color synthesis optical system has no cross dichroic prism. In the optical system shown in FIG. 3, however, the liquid crystal panel 15 and the field lens 46 are decentered from each other by the distance s, and so are the liquid crystal panel 16 and the field lens 47. For this reason, distortion due to this decentering poses a problem. The distortion makes it difficult to match the pixels of the three liquid crystal panels on the entire image. For this reason, this optical system is not fitted for application to a high-resolution liquid crystal projector used as, e.g., a computer monitor.
In the optical system shown in FIG. 4, the liquid crystal panels are arranged in the focused light beam. Therefore, the incident angle of illumination light changes depending on the position of the liquid crystal panel, resulting in contrast variations or color variations in the projected image. In addition, as no field lens is inserted between each liquid crystal panel and the projecting lens 48, distortion and curvature of field of the projecting lens are hard to correct. For this reason, again this optical system is not fitted for application to a high-resolution liquid crystal projector used as, e.g., a computer monitor.
In the color liquid crystal projector shown in FIG. 5, the transparent type liquid crystal in FIG. 2 is replaced with a reflection liquid crystal. The cross dichroic prism 42 is used not only as a color separation optical system but also as a color synthesis optical system, so the flat dichroic mirrors 34' and 35' can be omitted. However, this apparatus also uses the cross dichroic prism which is hard to manufacture.
Each of the color liquid crystal projectors shown in FIGS. 3 and 4 synthesizes three color light components through the entrance pupil of the projecting lens 48 and guides the synthesized light to the projecting lens 48. However, the color balance on the screen 23 depends on the arrangement of the mirrors 20 and 21. Since it is difficult to accurately arrange the mirrors 20 and 21, the color balance on the screen is unsatisfactory.
In the general projecting apparatus such as a color liquid crystal projector, the light amount distribution on the screen for the respective channels of the red light component (R light component), the green light component (G light component), and the blue light component (B light component) must be unified. However, the solid angles of the mirrors 20 and 21 subtended at given points on the liquid crystal panels 15 and 16 differ, so no uniform light amount distribution can be attained.
Also, various single plate projecting apparatuses using, as an optical modulation element, an optical modulation element using a liquid crystal to project color image information on a predetermined surface are proposed. In the single plate color optical modulation element using an optical modulation element comprising a liquid crystal, the black matrix for shielding, from light, the interconnection of an optical modulation control portion around the pixels of the optical modulation element (liquid crystal) has a large occupied area in the optical modulation element. This lowers the light utilization efficiency of the entire apparatus.
FIG. 63 is a view schematically showing such an optical modulation device 1200 using a liquid crystal to improve the light utilization efficiency. In FIG. 63, a microlens array 1121 is arranged in front of color filers 1151R, 1151G, and 1151B to focus illumination light W from a white light source onto the B, G, and R pixels of an optical modulation element 1120. With this arrangement, the light utilization efficiency of the optical modulation element 1200 is raised. This element also has a transparent substrate 1122 and a black matrix 1205 (FIG. 63).
The optical modulation element shown in FIG. 63 uses color filters as members for extracting color light components corresponding to the pixels of each optical modulation element. However, each color filter transmits only a light component having a predetermined wavelength in white light incident on each pixel, and therefore is useless for other wavelength components, so the light utilization efficiency is very low.